Domestic electric heater



Nov. 30, 1948. F. H. M CORMICK DOMESTIC ELECTRIC HEATER 7 Sheets-Sheet 1 Filed NOV 2, 1946 Nov. 30, 1948. F. H. McCORMlCK DOMESTIC ELECTRIC HEATER '7 Sh eets-Sheet 2 Filed Nov. 2, 1946 2 hsm will a llllllllll II IIIII lllllll IIIIII lllllllllfllllIlllllilll Nov. 30, 1948. H. M CORMICK v I 2,455,186

DOMESTIC ELECTRIC HEATER F1196 Nov. 2, 1946 Sheets-Sheet :5

Nov. 30, 1948. F. H. McCORMICK DOMESTIC ELECTRIC HEATER 7 Sheets-Shoot 4 III vial Filed NOV. 2, 1946 W ER KAW n 0 g H 3 1943- F. H. MCORMICK 2,455,135

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Nov. 30, 1948. F. H. 'M coRmcK I 2,455,186

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K 7 m J 9 w Patented Nov. 30, 1948 norms-no arscrarc nan-ma Francis 1!. McCormielr, Oakwood, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware ApplicationNovember 2, 1948, Serial No. 707,451 19 Claims. (01. 201-67) This invention relates to domestic appliances and more particularly to electric ranges.

An object of this invention is to provide an electric heater of improved efllciency and simplicity of construction.

Another object oi this invention is to provide an electric heater in combination with switch control therefor which cooperate in a novel manner.

Another object of this invention is to provide an improved and simplified method oi manufacturing an electric heater.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form is clearly shown.

In the drawings:

Fig.1 is a vertical cross-sectional view of one form of heater;

' Fig. 2 is a top plan view of Fig. 1;

Figs. 3 through 7 are longitudinal cross-sectional views 01' the heater shown in Fig. 1, in progressive stages of construction;

Fig. 8 is a transverse cross-section taken along the line 88 of Fig. 3;

Fig. 9 is a transverse cross-section taken along the line 9-9 of Fig. 4 r

Fig. 10 is an enlarged cross-section of the end terminal construction, and socket therefor, oi the heater shown in Fig. 1;

Fig. 11 is a diagrammatic representation of the heater shown in Fig. 1, in combination with an intermittent make and break switch;

Fig. 12 is a view similar to Fig. 11, but showing a modified form of the switch; 7

Fig. 13 is a view similar to Fig. 11, but showing a further modified form of the switch;

Fig. 14 is a plan view of a heater, somewhat similar to Fig. 1, but modified in certain respects;

Fig. 15 is a longitudinal cross-section of the heater shown in Fig. 14, and showing its combination with a switch;

Fig. 16 is a cross-section of the connecting means for the terminals of the heater shown in Fig. 14;

Fig. 17 is a diagrammatic view of a further modified form of heater, shown in combination with a switch therefor;

Fig. 18 is a cross-section of the connecting means for the terminals of the heater shown in Fig. 17;

Fig. 19 is a diagrammatic representation of the curving of the heater shown in Fig. 17;

Fig. 20 show the connections possible in the heater shown in Fig. 17 when all sections are energized;

Fig. 21 shows the connections possible when only two ections are energized;

Fig. 22 shows the connections when only one heater is energized;

Fig. 23 shows the control knob and dial for the switch indicated in Fig. 17;

Fig. 24 is a view, similar to Fig. 1, showing a further modified form;

Fig. 25 is a longitudinal cross-sectional view of a heater used in Fig. 24, taken along the line 25-25 of Fig. 26;

Fig. 26 is a cross-sectional view taken along the line 28--26 of Fig. 25;

Fig. 27 is a longitudinal cross-sectional view of a modified form of heater that may be used in a unit somewhat similar to Fig. 14, and taken along the line 21-21 of Fig. 28;

Fig. 28 is a cross-sectional view taken along the line 2828 of Fig. 27;

Fig. 29 is a longitudinal cross-sectional view of a modified form of heater that may be used in a unit as shown in Fig. 24, and taken along the line Iii-29 of Fig. 30;

Fig. 30 is a cross-section taken along the line 3030 of Fig. 29;

Fig. 31 is a longitudinal cross-section of a further modified form ofheater that may be used in a unit as shown in Fig. 24, and taken along the I line 3l-3l of Fig. 32;

Fig. 32 is a cross-section taken along the line 32-32 of Fig. 31; and

Fig. 33 is a cross-sectional view typical 01' a terminal construction which may be used with the heaters shown in Figs. 24 through 32.

A heater, according to my invention, includes a tubular sheath I0, which contains a. spiral resistance H, and a conducting rod iii. The spiral resistance II is connected at one end to a cylin dricai terminal i3, and at the other end to the conducting rod I! at the point it. If desired, insulating spacers, of porcelain or the like. are placed between the conduct ng rod l2 and resistance II, as indicated at IS, IS and IT, in order to maintain the rod and resistance in spaced relationship.

In manufacturing the heater, one end i8, of the sheath I0, is sealed by a ductile plug IS, in which one end 20 of the rod I2 is embedded. The rod I 2 is partially severed at 2|, between the end l8 and the junction point i4. 'The sheath is then filled with granular insulating material, such as MgO, and then the cylindrical terminal l3 and the end 22 01' the rod I! are secured to a plug 23,

which is not welded to the sheath Hi, all as shown in Figs. 3 and 8. Thereafter the sheath I is contracted radially and elongated longitudinally, as indicated in Figs. 4 and 9, in any well known manner, such as swaging or otherwise compressing. This operation compacts the insulation and also severs the rod- I2 at the point 2|, so that there is no electrical connection with the plug I9. Thereafter the end of the sheath l0, adjacent the plug 23 is cut away, as indicated in Fig. 5, to expose the cylindrical terminal l3. Thereafter a portion of the cylindrical terminal [3 is, in turn, cut away, as shown in Fig. 6, to expose the end 22 of the rod I2.

The terminals 22 and I3 thus exposed may be connected to a suitable electrical circuit by any one of several means. For example, an insulating disk 24 may be placed around the terminal l3, and against the end of the sheath i0, and a spirally threaded lamp socket member 25 may be secured to the terminal It, with a central contact button 26 electrically connected to the rod I2, and with the insulating disk 21 interposed therebetween. If desired, the button 26 may be formed by enlarging the end of the rod 82, or

it may be welded thereto. A suitable insulating disk 28 may also be placed inside of the terminal l3, to seal out moisture, in the same manner as is done by the disk 24. The lamp socket element 25 may cooperate with the other lamp socket member 30, which contains the threaded conducting sleeve 3| and the central contact member 32 electrically connected respectively with the lines 33 and 34.

The heaters shown in Figs. 3 through 9, after compacting the insulation, may be bent into a curve forming a substantially fiat cooking surface 35, and the top and/or bottom may be flattened as at 36 by a press or the like. The end 38a of the sheath it! depends at the central portion of the heater thus formed, and cooperates with the lamp socket member 30, into which it may be screwed similarly to a lamp. The sheath I0, after being curved as shown in Figs. 1 and 2, rests loosely upon or may be welded, by projection welding or the like, to the transverse channel members 3'l and 38, which are adapted to rest on a flanged metallic cup 38, provided with a flanged central opening w, and having a flange 4| resting on the depressed flange t2 formed in the top surface 43 of the range. If desired, a

' cone-shaped guard 44 may be attached to the sheath l0, above the opening 40, to prevent spillage through the opening 40. The lamp socket member 30 may be clamped to the support 45 on the range.

The heater heretofore described may be energized by an intermittent make and break switch as shown in Fig. 11. The line 33 may be connected to a stationary contact 50, while the line 34 may pass through a heater M, of low resistance, which is connected to the contact 52 carried by a thermostatic bimetal blade 53, which bends upward when heated. A rotatable handle 54, in front of a stationary dial 55, operates a shaft, linkage or the like 58, which actuates the cams 51 and 58. The cam 51 is provided with a protuberance 59 to open the blade 80 against the compression spring 8| to open the contact 82 from the contact 50, in the off position of handle 54.. The blade 60 is connected to a power line 83. The cam 58 is spirally shaped, as shown, in order to allow the blade 84 to be pushed gradually upward by the compression spring 85, as the handle 54 is turned clockwise from the Off 4 position. This clockwise movement of handle 54 allows blade 64 and contact 88 to rise gradually until 66 is brought into contact with 52 the necessary distance to establish a circuit with the power lines 61 and 83. As the resistances II and 5| become hot, the thermostatic blade 53 bends upward until the contact 52 is lifted from contact 88. This establishes a break interval of time, during which the resistance 5| and thermostat blade 53 cool to the point where the blade 53 bends downward to make contact between 52 and 68 to begin another heating cycle. Thus an adjustable make and break cycling interval is established. In the off position of the handle 54, the protuberance 59 retains one side of the line open at 50-82, while the other side of the line is also retained open because the portion 88 of the cam 58 maintains the contact 88 open below the lower limit of the downward travel of contact 62, which limit is established by the stop member 69. The shape of cam 58 moves the blade 64 an adjustable distance upward. This makes an adjustable heating cycle,

' adjusted by the position of handle 54.

In the modification shown in Fig. 12, the resistance H, and line 33 are connected to the stationary contact 10 and to the rotatable contact H. The contact ll moves over the rheostat 12, which is connected to a low resistance heater 13 adjacent to a thermostatic bimetal blade 14, carrying contact 15, to which the other end of resistance I3 is connected. The line 34 is also connected to the contact I5. The blade 14 mo .5 downwardly when heated. The rotatable handle 76, movable in front of the stationary dial l1, actuates the shaft or linkage 18, which turns the cam 19 and blade 1 l. The protuberance opens the blade 80a and contact 8!, in the off position of the handle it, to disconnect the line 33 from the power line 82. The blade 83, carrying contact 84, is interlocked at with the blade 80a and contact 8|, so that the line as is also disconnected at 15 and 84 in the off position of the handle 16. The upward movement of the thermostatic blade 14 is limited by the insulated stop 81 to prevent closing of the line in the off position. In this modification, the handle 16 is moved counterclockwise from the off position, and thus interposes more of the resistance of the rheostat I2 in the circuit of heater [3 as the handle 16 is moved to higher and higher temperature positions.

In the operation of the modification shown in Fig. 12, the handle 16 is moved counterclockwise to some position, such as 400. The protuberance 80 is moved away to allow the closing of the contacts 10, 8| and I5, 84. This establishes parallel circuits through resistance H and the combination of part of rheostat 12 with heater 13. As the heater 13 becomes heated, the blade I4 opens the contact 15 at a suitable time interval, established by the amount of resistance interposed at the rheostat 12. The more the handle 18 is turned counterclockwise, the more resistance is interposed at I2, and therefore it The handle actuates the shaft or linkage 92,-

connected to the cams 93 and 94. The cam 93 has the protuberance 95, effective in the off posiau ios tion, to open the contacts 88 and 51, as heretofore described. The cam 84, is eflective to move the blade 88 adiustably downwardly, similarly to blade 54 heretofore described against the compression spring 980. The blade 98 is urged upwardly about a fulcrum I by the spring IOI against a slowly rotating cam I02 which is geared by gears I 08 and I04 to the synchronous motor I05. The line 38 is connected to the motor I05, and the other terminal thereof is connected to the power line I05. The blade 98 is also connected to the power line I05 at I0'I.

In the operation of Fig. 13, rotation of handle 80 clockwise from the off position closes the contacts 98, 51 and also the contacts I08 and I08, carried by. the blades 98 and 99 respectively. This establishes parallel circuits through the resistance II and clock I05 from the power lines I08 and MM. Theslow rotation of the cam I02 establishes intermittent make and break action at contacts I08 and I00. The interval thereof is determined by the position of the handle 80 and the cam 84. As the handle 90 is moved clockwise to higher and higher value the blade 98 moves higher and higher to maintain the contacts I08 and I05 closed for longer intervals of time.

In the modification shown in Figs. 14, and 16, the sheath IIO contains a cylindrical terminal III at one end and another cylindrical terminal H2 at the other end. The terminals III and H2 are connected to the ends of the spiral resistance H5. The conducting rod II4 passes through the cylindrical terminal I I2 and is electric-ally connected at an intermediate portion of resistance II8 by means of the conducting plug 5. The heater may be assembled, filled with granular insulation I I8, compacted by radial contraction and longitudinal elongation, in any of the well known manners, as by swaging. Thereafter it may be bent into a curve forming a substantially flat cooking surface, and the imp thereof may be flattened as at may be welded to the transverse channels I28 and I29, which in turn are supported on a ring I80 substantially as disclosed in the patent to Mc- Cormick 2,320,041, granted May 25, 1943. The terminals III and H2, and the rod 4 may be connected to the electrical connectors H1, H8 and H9. so that they may be connected to the switch means I and from thence to the power lines I2I', I22 and I23. The switch means I20 may establish various heating circuits such as disclosed in the patent to McCormick 2,259,258 patented October 14, 1941.

I21. and the sheath In the modification shown in Figs. 17 through 22, the sheath I50 is provided at its ends with cylindrical terminals I5I and I52. A spiral resistance I53 has its ends connected to the terminals I5Iand I52. The conducting rods I54 and I 55 pass through the terminals I5I and I52 respectively and are electrically connected to the resistance I53 at intermediate points by means of the conducting plugs I56 and I5! respectively. The sheath I50 may be packed with granular insulating material and may be radially contracted and longitudinally elongated in the well known manner, as by swaging. The terminals HI and I52 and conducting rods I54 and I55 may be connected to the connecting appliance shown in Fig. 18 to connect them respectively with the electrical lines I58, I59, I50 and IBI, as indicated in Fig. 17. These lines are connected to the rotatable contact blades I62 carried by a shaft I58 which is actuated by the handle I64. If

which has been indicated desired. the shaft I58 may be provided with the snap-acting mechanism I55,v to insure quick movement from the various positions. The contact points I56 are connected to one power line, for convenience as plus, although it obviously and preferably may be one of the live lines of an alternating current suDl' y-. Other contacts I61, indicated by a "minus sign, are connected to the other live line of the alternating current supply. Other con: tacts I 68 are connected to the neutral line, which has been indicated for convenience with an N. Other contacts, indicated nected to any power line. Any type of well known switch. which may be actuated by a rotatable handle to establish the circuits indicated, may be used. If desired, it may be of the reciprocating blade type, actuated by proper cams in lieu of the rotatable blades. The turning of the handle from the off position to the various other positions establishes the circuits indicated in Figs. 20, 21 and 22.

The heater may be bent into a curve forming a top surface substantially the same as in Fig. 14, with the exception that it has four leads instead of three.

In the modification shown in Figs. 24, 25 and26, a tubular sheath I is closed at one end by the ductile plug I8I. v Two spiral resistances I 82 and I83 are placed in parallel relationship within the sheath I80. Conducting rods I84 and I 85 are placed within the resistances I52 and I 83. The ends of the rods I84 and I 85, stone end of the sheath I80, pass through cylindrical conductors I86 and I'8'I. The conductors I86-and I81 are connected to resistances I82 and I83 respectively. The other ends of the rods I84 and I85 originally are connected to the plug I8I,-similarly to the construction shown in Figs. 3 and 8. After the sheath I80 is elongated, as by swaging, the rods I84 and I85 are severed at I88 and I89, where they are connected to the resistances I82 and I83 respectively. The rods I84 and I85 are spaced from the resistances I82 and I83 by the insulating plugs I90. The cylindrical connectors I83 and I81 are positioned by the insulating plug I9! which is held in place by inwardly striking sheath I80. 'The modification shown in Figs. 24, 25 and 26 is assembled and manufactured substantially in the same manner as disclosed with respect to Figs. 3 through 9, with the exception that the heater contains two resistances instead ofone, and that the terminal is connected'to a structure somewhat similar to that shown in Fig. 18, modifled as is obvious. This construction provides two resistances which may be connected to a switch structure and circuit substantially as shown in my Patent Number 2,259,258, patented October 14, 1941, or to any other type of switch capable of connecting the heaters independently or in series to the full voltage or half voltage of a three line power source.

In the modification shownin Figs. 27 and 28, a tubular sheath 200 is provided with two parallel spiral resistances 2M and 202, which are secured t1 the cylindrical conductors 205. The conductors 203 through 206 v pass throne-h insulating plugs 20! and 208, similar to plug I9I heretofore described. This heater may be assembled and swaged in the general manner heretofore described, and each end may be connected to a terminal construction substantially as shown in Fig. 33. Such terminal construction may be a single one, having four bayonet connections, or it may comprise two separate conat I65, are not con 203, 204 20.5,and

accuse nectors, each having two bayonets. The heater may be bent into a unit substantially as shown in Fig. 14,,but having four connections. This provides two entirely independent resistances, 2M and 202, each of which may be energized across the full voltage or the half voltage in parallel or series by any suitable switch construction desired, or as described in my Patent Number 2,259,258.

In the modification shown in Figs. 29 and 30, the sheath 2! contains two resistances 2H and 212. The resistance 2 has its two ends connected to cylindrical connectors M3 and 2H, and its intermediate portion 2l5 bent reversely, so that the current may fiow from connector 213 to connector 2M through the resistance 2! i. Similarly the resistance 2 l2 has its ends connected to cylindrical connectors 2l6 and 2H, and its intermediate portion 2! reversely bent, so that current can flow from connector 216 to 2 ll. One end of the sheath 210 is provided with a ductile plug H9, and the other end is provided with the insulating plug 220, similar in construction to plug l9l. This heater may be bent into a unit substantially as shown in Fig. 24 but being more rectangular in cross-section, as indicated. in Fig. 30. One of the fiat sides is placed at the top of the unit. The conductors 203, M4, 215 and Bill may be connected to a plug substantially as shownin Fig. 33. This heater provides two independent resistances, which may be-energized at full voltage or half voltage in parallel or in series, by suitable switch construction, to give a large number of combinations, or as described in my Patent Number 2,259,258.

in the heater shown in Figs. 31 and 32 the sheath 230 contains spiral heaters 23$] and 232. The heater 223i is connected to cylindrical'conductors 233 and 236 respectively. The heater is connected to cylindrical connectors 235 and 236. The intermediate portion 231? of heater 223i is a reverse bend, as indicated in Fig. 31. The intermediate portion 232 of heater 232 is also a reverse bend adjacent the bend 2M, but completely insulated therefrom. The sheath 2% is provided with a ductile plug 232, and an insulating plug 2% substantially or" the same construction as heretofore described with respect to Figs. 29 and 30. The heater shown in Figs. 31 and 32 may be bent into a unit substantially as shown in Fig. 23, but having cross-section as indicated in Fig. 32. One of the straight edges 2M of Fig. 32, however, may be the top surface or the unit shown in Fig. 2 The conductors 233 through 236 may be connected to a connector construction substantially as shown in Fig; 33. The heat= ers of this unit may be connected to a switch as described with respect to Figs. 29 and 30.

The connector shown in Fig. 33 may comprise an insulated casing 25d, through the end of which the three or four wire cable 25H passes. An insulated disk 252 is provided with bayonet conductors 253 which are adapted to engage the end of the cylindrical conductors 203 and 286, 2 it, 2 i t, 2H, 2H, and 233 through 236, as is evident. The casing 250 may be made in two longitudinal halves, which may be secured at the ears 254 by nuts and bolts, not shown, for final assembly, as is obvious, Each longitudinal half, has a semicylindrical opening 255, for the reception or the conductors of the heater, and a semi-cylindrical opening 256 for the reception of cable 25!.

While the form of embodiment of the invention as hereinidisclosedconstitutes a preferred form. it is to be understood that other'forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In combination, a tubular sheath having two ends, a first cylindrical terminal at one end, a second cylindrical terminal at the other end, a

spiral resistance in said sheath connected to said terminals, and a conducting rod passing through said first cylindrical terminal and connected to an intermediate point on said resistance.

2. In combination, a tubular sheath having two ends, a first cylindrical terminal at one end, a second cylindrical terminal at the other end, a spiral resistance in said sheath connected to said terminals, a conducting rod passing through said first cylindrical terminal and connected to an intermediate point on said resistance, and another conducting rod passing through said second cylindrical terminal and connected to said resistance intermediate said point and said second cyiindrical terminal.

3. In combination, a tubular sheath having two ends, a first cylindrical terminal at one end, a second cylindrical terminal at the other end, a spiral resistance in said sheath connected to said terminals, and a conducting rod passing through said first cylindrical terminal and connected to an intermediate point on said resistance by means of a cylindrical connector of an external diameter substantially the same as the internal diameter of said spiral resistance.

4. In combination, a tubular sheath having two ends, a first cylindrical terminal at one end, a second cylindrical terminal at the other end, a spiral resistance in said sheath connected to said terminals, a conducting rod passing through said first cylindrical terminal and connected to an intermediate point on said resistance, and another conducting rod passing through said second cylindrical terminal and connected to said resistance intermediate said point and said second cylindrical terminal by means of a cylindrical connector of an external diameter substantially the same as the internal diameter of said spiral resistance.

5. in combination, a tubular sheath. having two ends, a first terminal at one end, a second terminal at the other end, a spiral resistance in said sheath connected to said terminals, and a conducting rod passing said first terminal and connected to an intermediate point on said resistance.

6. in combination, a tubular sheath having two ends, a first terminal at one end, a second terminal at the other end, a spiral resistance in said sheath connected to said terminals, 9. conducting rod passing. said first terminal and connected to an intermediate point on said resistance, and another conducting rod passing said second terminal and connected to said resistance intermediate said point and said second terminal.

"I. In combination, a tubular sheath having two ends, a first terminal at one end, a second terminal at the other end, a spiral resistance in said sheath connected to said terminals, 9. conducting rod passing said first terminal and connected to an intermediate point on said resistance, and a switch connecting said terminals and conducting rod variously to power lines.

8. In combination, a tubular sheath having two ends, a first terminal at one, end, a second terminal at the other end, a spiral resistance in said sheath connected to said terminals, a conducting rod passing said first terminal and connected to an intermediate point on said resistance,

sheath being bent into a curve forming a substantially fiat cooking surface with said terminal construction depending from a central portion.

10. In combination, a tubular sheath having a terminal construction at one end and being sealed at the other end, and a resistance in said sheath connected to said terminal construction, said sheath being bent into a curve forming a substantially flat cooking surface with said terminal construction depending from a central portion, said terminal construction including a pair of co-axial and longitudinally spaced connectors.

11. The method of manufacturing a tubular sheath heater which comprises surrounding a rod conductor with a spiral resistance and connecting said resistance near one end of said rod conductor, partially severing said rod conductor intermediate the connection and said end placing said rod conductor and resistance in a tubular sheath, securing said one end of said rod conductor to a plug secured at one end of said sheath,

surrounding the other end of said rod conductor with a tubular connector connected to said re sistance, securing said tubular connector and said other end of said rod conductor to another plug resting against the other end of said sheath, filling said sheath with granular insulation, contracting said sheath radially and thus compacting said insulation while elongating said sheath and completing the severance of said conductor where partially severed, and cutting said sheath away at the outer end of said tubular connector to produce connecting means for said rod conductor and connector.

12. In combination, a tubular sheath sealed at one end, a rod conductor and spiral resistance in said sheath connected together near said one end and electrically connectible at the other end of said sheath, an intermittent make and break switch connected to said rod and conductor, and

manual adjusting means to initiate the intermittent making and breaking of said switch and to adjust the cycling interval thereof.

13. In combination, a tubular sheath closed ing bent into a curve forming a substantially flat cooking surface, and a switch connected to said resistances to impose selectively the full voltage of a three wire power source on one of said resistances and the half voltage on the other resistance.

16. The method of constructing a tubular sheath heater which comprises closing one end of said sheath, inserting two spiral resistances with return bends near said one end, inserting granular insulation into said sheath to space said resistances throughout the length of said sheath, compacting said insulation, and bending said sheath into a curve forming a substantially flat cooking surface.

17. In combination, a tubular sheath having two ends, a first cylindrical terminal at one end, a second cylindrical terminal at the other end, a spiral resistance in said sheath connected to said terminals, a conducting rod passing through said first cylindrical terminal and connected to an intermediate point on said resistance, said sheath bein bent into a curve forming a substantially flat cooking surface, with said ends of said sheath extending downwardly, and electrical connecting means .for said terminals and conducting rod attached to said ends.

18. An electrical heater comprising, a tubular sheath having a closed end and an open end, a

tubular terminal connector at said open end, a'

helical resistor in said sheath having one end connected to said tubular terminal connector and its other end adjacent said closed end, a conductor spaced from and passing through said tubular terminal connector and connected to said resistor adjacent said closed end, and compacted granular insulating material filling said sheath.

19. The method of manufacturing a tubular sheath heater which comprises surrounding a conductor with a helical resistor and connecting said resistor and conductor adjacent one end of said conductor, weakening said conductor at a point adjacent said one end, inserting said conductorand resistance in a tubular sheath having one closed end and securing said one end of said conductor to the closed end of said sheath, passing the other end of said conductor through a tubular terminal connector and connecting said helical resistor to said tubular terminal connec- 0 tor, placing said tubular terminal connector at at one end, two spiral resistances extending into saidsheath each with two ends nectible at the other end of said sheath, granular insulation surrounding said resistances, said sheath being bent into a curve forming a substantially fiat cooking surface.

14. In combination, a tubular sheath closed at 6 one end, two spiral resistances extending into said sheath each with two ends electrically connectible at the other end of said sheath, granular electrically coninsulation surrounding said resistances, said sheath being bent into a curve forming a sub-' stantially flat cooking surface, and a bayonet joint connector at said other end of said sheath,

15. In combination, a tubular sheath closed at one end, two spiral resistances extending into said heater each with two ends electrically connectible at the other end 01' said sheath, granular insulation surrounding said resistances, said sheath bethe open end of said sheath, filling said sheath with granular insulating material, compacting saidinsulating material and severing said first named conductor at said weakened point, as a result of the elongation of the sheath which occurs as a result of the compacting process.

FRANCIS H. MCCORMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number I Name Date 1,020,439 Norwood Mar. 19, 1912 1,124,849 Brush Jan. 12, 1915 1,378,324 Clark et al May 17, 1921 1,394,518 Abbott Oct. 25, 1921 1,474,723 Levinson Nov. 20, 1923 1,667,857 Harpster et al. May 1, 1928 1,684,184 Kin Sept. 11, 1928 2,094,480 Vogel Sept. 28, 1937 2,390,577 Ferris Dec. 11, 1945 

